"Too many open files" error, regardless of size parameter

I am using grequests to test the performance of my service. Both the service and the machine from which I start the requests are inside Amazon EC2. It seems that I cannot start more requests than ulimit -n, even though I explicitly specify the size parameter for map() / imap()

My setup is roughly like this:

headers = {'Content-type': 'application/json', 'Accept': 'text/plain'}
params = [json.dumps({'url': urls[i]}) for i in urls]
reqs = [grequests.post(SERVICE_URL, data=params[i % len(params)], headers=headers)
            for i in xrange(no_requests)]
res = grequests.imap(reqs, size=200)
for r in res:
    ...
    r.close()

Doesn’t the size parameter here tell grequests that it should issue no_requests, 200 at a time?

[cyberstip]

For posterity, just adding a session to the request seems to fix the issue (as @rtdean mentioned):

session = requests.Session() reqs = (grequests.get(url, session=session) for url in urls) results = grequests.map(reqs, size=50)

[amitsquare]

Please do mention using Session Object in README .As till you complete system shutdown , user won’t be searching the issue & end up here on this issue thread .